There is a constant effort to improve the efficiency of blades used on lawnmowers and in particular on powered lawnmowers not only for cutting grass and the like, but also for mulching purposes. In my U.S. Pat. No. 5,581,987 I disclosed a mower blade which can be utilized with both cutting and mulching mowers.
In general, a rotary lawnmower includes a mower blade mounted below the deck which rotates about an axis. The free end of the blade comprises a cutting edge. Typically the cutting edge would be at an angle no greater than 30°. Attempts have been made to improve the efficiency of the cutting edge by forming notches or irregularities in the exposed portion of the cutting edge. These notches or irregularities are also at a small angle and sharpened so that the notches or irregularities are part of the cutting edge and likewise perform the cutting function. Examples of these techniques are described in U.S. Pat. Nos. 2,869,311, 3,022,621, 3,214,896, 3,452,524, 3,949,541, 3,998,037 and 5,899,053. U.S. Pat. No. 4,617,788 shows a variation wherein a mulching blade is provided with a pair of notches in the cutting edge. Each of the notches forms an opening which is substantially an equilateral triangle.